The entire premise of callbacks is that threads were a mistake because they broke sequential reasoning and control.

JK, obviously callbacks became prominent as a result of folks looking for creative solutions to the C10K[0] problem, but threads have a long history of haters[1][2][3].

[0] https://en.wikipedia.org/wiki/C10k_problem

[1] https://brendaneich.com/2007/02/threads-suck/

[2] https://web.stanford.edu/~ouster/cgi-bin/papers/threads.pdf

[3] https://www2.eecs.berkeley.edu/Pubs/TechRpts/2006/EECS-2006-...